METHODS AND APPARATUS FOR DIAGNOSING FAULTS OF A VEHICLE
A rubber cleat is instrumented with two triaxial accelerometers to measure the multi-directional response of the cleat due to the forces within the tire footprint of a ground vehicle. The cleat data is used to detect faults in the front and rear suspension in addition to the wheel tire despite variability in the data. This offboard diagnostic technique is proposed to enable condition-based maintenance.
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This application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/098,995, filed Sep. 22, 2008, entitled INSTRUMENTED CLEAT, incorporated herein by reference.
FIELD OF THE INVENTIONVarious embodiments of the present invention pertain to methods and apparatus for determining a change in the condition of a vehicle, and in particular to the use of ground-based sensors for finding faults in a wheeled vehicle.
BACKGROUND OF THE INVENTIONThe U.S. Army is pursuing technologies that will enable Condition-Based Maintenance (CBM) of ground vehicles. Current maintenance schedules for ground vehicles are determined based on reliability predictions (e.g., mean time to failure) of a population of vehicles under anticipated operational loads; however, vehicles that experience component damage often lie in the tails of the reliability distribution for a given platform. For example, a certain group of vehicles may be deployed to operate on a harsh terrain that is particularly taxing on the mechanical components in the suspensions or frames of those vehicles. Operation & support costs for military weapon systems accounted for approximately ⅗th of the $500B Department of Defense budget in 2006 (Gorsich, 2007). To ensure readiness and decrease these costs for ground vehicle fleets, health monitoring technologies are being developed to assess the reliability of individual vehicles within each fleet.
Based on a review of the open literature including Technical Note 85-3 (Thomas, 1985) on ground equipment reliability issues associated with materials, it can be concluded that the most common faults occur in wheel ends (tires, brakes), suspensions, and frames. For example, Aardema (1988) discussed a ball joint failure in the HMMWV (High Mobility Multi-purpose Wheeled Vehicle). Braking systems have also experienced wear most likely due to severe operating conditions such as overheating. Reliability issues in suspensions due to wheel weights have also been reported (FORSCOM, 2004). Faults in the HMMWV body chassis and frame have also been reported in reliability centered maintenance studies (Lasure, 2004).
The response of the HMMWV to a cleat excitation has been studied by Faller, Hillegass, and Docimo (2003). The response of the center of mass, driver, and left and right wheel of the HMMWV was experimentally determined with accelerometers during a road test over a 4 inch high semicircle cleat. The road test was conducted at vehicle speeds of 5 and 14 mph. The speed was found to affect the response of the vehicle.
Many health monitoring systems usually place all measurement instrumentation on the vehicle itself to measure vehicle responses. However, Champoux, Richard, and Drouet (2007) have used an instrumented bump to study the wheel response of a bicycle. The bump was instrumented with biaxial force transducers. The rest of the bicycle was instrumented with strain gages and accelerometers to measure the cyclist's comfort.
Dynamics-based health monitoring can be used to identify faults because vibrations are a passive source of response data, which are global functions of the loading and mechanical properties of the vehicle. One way of detecting faults in mechanical equipment, such as the suspension and chassis of a ground vehicle, is to compare measured vibrations to a reference (or healthy) signature to detect anomalies. In order to make this comparison, a library of vibration signatures must be developed and categorized according to the operational conditions of the vehicle (speed, terrain, turning radius, etc.).
There are two principle difficulties with this approach. First, the number of datasets required to develop a library of possible healthy signatures extracted from an N-dimensional sensor suite on a vehicle given M terrains on which that vehicle can operate is of order MN (Bishop, 1990). For example, 6 sensors over 10 terrains would require that one million datasets be used to establish a fully populated reference set for fault detection. If 240 datasets are acquired each day on average, then it would take 11 years to develop this library of healthy signatures for each individual ground vehicle. This large number of datasets would be needed to characterize the normal operational response of the vehicle due to the non-stationary nature of the loading and the inability to control these loads in operation. Second, many vehicles are not equipped with sensors nor the acquisition systems to acquire, process, and store data; therefore, to implement health monitoring for condition-based maintenance, one needs to overcome the economic and technical barriers associated with equipping ground vehicles to continuously monitor their responses.
What is needed is a system that can be more user friendly, simplified, more reliable, and/or require less data. Various embodiments of the present invention provide some or all of the aforementioned aspects.
SUMMARY OF THE INVENTIONOne aspect of some embodiments of the present invention pertains to a portable instrumented device that is part of a roadway. As a vehicle drives over the device, the response of the device to the vehicle is measured.
Another aspect of some embodiments pertains to a method of diagnosing the condition of a mechanical system. An instrumented, resilient device is placed between some portion of the system and the system's environment. The sensor can measure various loads, disturbances, forces, and the like that are imparted by the system onto the environment.
Yet another aspect of other embodiments of the present invention pertains to the placement of a device on a roadway, and driving a vehicle over the device. The device elastically deforms in shape as the vehicle traverses over it. One inventive method further includes sensing the deformations, and relating the deformations to motion of the device or the force exerted on the device on the vehicle.
Yet another aspect of other embodiments of the present invention pertain to various methods for comparing the response of an instrumented roadway on a first, later occasion to the response of the same vehicle on instrumented roadway at an earlier occasion. The responses preferable include data responding to movement of the roadway (such as with a resilient section of roadway) in terms of the time domain or frequency domain.
in yet another aspect, a diagnostic cleat has been developed for measuring the dynamic forces exerted on the wheels of a ground vehicle as the vehicle traverses the cleat. By comparing the responses obtained from the various wheels with one another and with baseline data corresponding to “healthy” wheels, faults in the wheel end and suspension can be detected. Further, the responses can be used to diagnose other problems in the vehicle, such as a cracked or bent subframe, defective motor mount, and others. The diagnostic cleat can also be utilized for (a) estimating reduced-order dynamic models of the vehicle and (b) estimating terrains traversed by the vehicle if on-board sensors 27 are used to complement the off-board sensors 60 in the cleat.
One embodiment of the present invention pertains to a multi-stage model estimation, terrain estimation, and damage estimation approach as it applies to a simplified model of a ground vehicle. The approach uses an over-determined set of input-output equations to minimize the error across the set of equations that define the vehicle model. This model relates the base excitation spectrum supplied by the cleat 50 for a given vehicle speed to the response spectra that are acquired on the vehicle (sprung and unsprung masses) as it traverses the cleat while the vehicle exits and enters a motor pool. This model can also be stored on-board the vehicle as it traverses various terrains over the course of the mission.
As the vehicle conducts its mission, the model is used together with the measured vehicle responses to estimate the terrain base excitation spectrum to the wheel 24. This estimate of the base excitation can then be used for at least two purposes in some embodiments. First, it can be used as a means of estimating the usage of the vehicle through rainflow fatigue analysis. Second, the estimate of the base excitation can be used together with the vehicle model to update the model thereby providing an indication of the degradation that is experienced by the vehicle over the course of the mission.
It will be appreciated that the various apparatus and methods described in this summary section, as well as elsewhere in this application, can be expressed as a large number of different combinations and subcombinations. All such useful, novel, and inventive combinations and subcombinations are contemplated herein, it being recognized that the explicit expression of each of these combinations is excessive and unnecessary.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. At least one embodiment of the present invention will be described and shown, and this application may show and/or describe other embodiments of the present invention. It is understood that any reference to “the invention” is a reference to an embodiment of a family of inventions, with no single embodiment including an apparatus, process, or composition that must be included in all embodiments, unless otherwise stated.
The use of an N-series prefix for an element number (NXX.XX) refers to an element that is the same as the non-prefixed element (XX.XX), except as shown and described thereafter. As an example, an element 1020.1 would be the same as element 20.1, except for those different features of element 1020.1 shown and described. Further, common elements and common features of related elements are drawn in the same manner in different figures, and/or use the same symbology in different figures. As such, it is not necessary to describe the features of 1020.1 and 20.1 that are the same, since these common features are apparent to a person of ordinary skill in the related field of technology. Although various specific quantities (spatial dimensions, temperatures, pressures, times, force, resistance, current, voltage, concentrations, wavelengths, frequencies, heat transfer coefficients, dimensionless parameters, etc.) may be stated herein, such specific quantities are presented as examples only. Further, with discussion pertaining to a specific composition of matter, that description is by example only, does not limit the applicability of other species of that composition, nor does it limit the applicability of other compositions unrelated to the cited composition.
It is understood that various embodiments of the present invention can utilize many different configurations of cleats. Some, but not all, of these different cleat configurations are described with relation to an integer number (XX) in front of the number 50 (XX50), and also some, but not all, are referred to with prime (′) and double prime (″) suffixes. It is understood that in many cases cleats with various prefixes and suffixes can be substituted in different embodiments for cleats having different prefixes or suffixes. Further, it is understood that reference to “cleat 50” in this specification includes reference to all cleats described herein as would be understood by a person of ordinary skill in the art.
It is further understood that reference to a “wheel” is a reference to the rotating device that supports the vehicle from the roadway, terrain, runway, factory floor, or other vehicle path. For example, in an automobile it is understood that reference to a “wheel” can be construed as reference to the tire, especially in those situations in which there is reference to driving the wheel over a cleat. However, various embodiments of the present invention are not so limited, and include those vehicles having metallic wheels in contact with a roadway (including trains in which the “roadway” is a train track), industrial vehicles such as Bobcats® (in which substantially solid rubber tires are mounted on metallic wheels, and in which the roadway is an aisle within a factory), and airplanes (in which a pneumatic tire is in contact with a roadway that is a runway). Further, it is understood that reference to a “roadway” is reference to any surface over which the vehicle is being driven.
Although reference is made herein to instrumented cleats that are portable, it is understood that portability is not a requirement. In some embodiments of the present invention, the instrumented cleat is a resilient change in elevation of the roadway, either a bump or trough, that is substantially built into the roadway, and which is generally non-portable. The term “resilient” is a generalized reference to Hooke's law, such that the material and/or mechanical configuration is chosen such that there is a measurable displacement within the frequency ranges of interest to the traversing of a vehicle over the cleat. For example, in some embodiments a cleat can be fabricated from an elastomeric material that is molded in place onto a roadway, especially a molded cleat positioned within a channel cut into the surface of the roadway. As other examples, any of the cleats shown in
Reference is made herein to means for measuring a response of a roadway to a vehicle, which because of Newton's relationships pertaining to action and reaction, is the same a means for measuring the response of the vehicle to the roadway. Such means for measuring response pertains to any of the cleats shown and described herein, along with any of the movement sensors shown and described herein. As but two examples, means for measuring response include a cleat 50 including a single axis accelerometer, and further include a cleat 350 including triaxial displacement or strain measurements. Further, means for changing the elevation of a vehicle refer to any of the cleats shown and described herein, as well as their equivalents. As but one example, means for changing the elevation of a vehicle include a plurality of cleats 250 arranged in patterns 852′ and 852″. In addition, as used herein, means for sensing include any of the movement sensors described herein, and further any sensors that can detect motion of or force upon a resilient elevational change of a roadway, and their equivalents. As nonlimiting examples, means for sensing includes accelerometers, velocity sensors, position sensors, strain gages, force transducers, and the like, whether operating electromechanically, electro-optically, or in any manner.
It is useful to consider how rotating machinery diagnostic systems function. In these machines, the repetitiveness of the operating load for a machine operating at constant speed makes it relatively easy to identify faults in the bearings, shaft, etc. In wheeled ground vehicles, loading varies significantly as mentioned above. If loads acting on the vehicle could be fully measured or controlled in terms of the terrain input motions and/or spindle forces/moments, fault identification in wheeled vehicles at the component level would be more straightforward. Mechanical properties that determine the vehicle condition could be extracted from data if loads could be controlled. There are at least two approaches to overcome some of the difficulties mentioned above:
(1) If a vehicle cannot be equipped with sensors, then an instrumented diagnostic cleat 50 is proposed in some embodiments as illustrated in
In one aspect of the present invention, the general configuration of cleat 50, both with regards to geometry and placement and type of sensors, is substantially the same as a cleat that was used for a previous test. For example, as shown in
(2) If a vehicle can be equipped with sensors, then a “reference-free” approach to data analysis is used to compare similar response pathways on the vehicle to identify mechanical anomalies. For example, the vertical and tracking responses of the left wheels can be compared to the same responses of the right wheels to determine if the front/rear wheels exhibit anomalies. This approach could be effective because it diminishes the need for reference signatures to identify faults.
Some of the first aspects of the first approach includes: the cleat 50 is portable making it practical for field use; cleat can be engineered to control the amplitude and frequency of the input imparted to the vehicle wheels allowing for more targeted diagnostic results; vehicle speed traversing the cleat can be controlled; the configuration of cleats can be designed to develop specific tests for certain subsystems; sensors are installed within the cleat (or proximate to the cleat such that the sensors provide a response related to movement of the cleat) rather than the vehicle providing greater reliability; and algorithms for analyzing response data from the cleat can be less complex than for on-vehicle diagnostic algorithms, which must address non-stationary data.
An instrumented diagnostic cleat according to one embodiment of the present invention can overcome the economic and technical barriers associated with onboard health monitoring systems. The diagnostic cleat measures the dynamic response of the vehicle as it traverses the cleat at a speed. Then the dynamic response is compared to a baseline reference (or healthy) response to detect anomalies, which correspond to faults within the vehicle. The diagnostic cleat addresses some of the various aspects associated with variations in the terrain assuming a fixed vehicle speed and cleat profile. The cleat can also eliminate the need for onboard vehicle equipment, and in some embodiments it is portable so one cleat can diagnose a fleet of vehicles.
Various embodiments of the present invention contemplate driving a vehicle over an instrumented change in elevation, and measuring the response of the change in elevation. Preferably, the vehicle is driven over the elevational change at a particular predetermined velocity within a range of velocities. The range of velocities can be selected to correspond to the baseline dataset to which the potentially faulted vehicle responses will be compared. As one example, and of situations in the baseline data is from a family of substantially similar vehicles, the range of velocities may be relatively substantial, and contemplation that at the time of testing the driver of the specific vehicle is in a future, unknown situation. In such cases, the baseline or family data may be taken over a fairly wide range of velocities (perhaps five mph to twenty mph), with baseline response data recorded and processed as a function of the velocity of the baseline vehicle (for example, baseline data can be taken in one mph increments over the range). However, in yet other embodiments, the baseline data may have been taken relatively recently, in which case it may be preferable to have a rather narrow predetermined range (as one example, +/−1 mph of range about a particular target velocity). Various embodiments of the present invention contemplate providing feedback to the driver if he is outside the predetermined range, such that the driver performs a second attempt at creating a dataset.
In yet other embodiments, dataset can be taken at any velocity, and the dataset can be subsequently normalized or adjusted for velocity effects. As one example, it may be possible to adjust a dataset (either a baseline dataset or a specific dataset) in a linear, inverse, or squared relationship relative to velocity. The later may be useful in those situations where the response of the cleat sensors corresponds most directly to the kinetic energy of the vehicle. Further, such normalizations and adjustments can be of one type at frequencies proximate to a known resonant frequency of the vehicle system, and of a different type at frequencies inbetween known resonant frequencies. As non-limiting examples, a time-domain peak-G response of a specific dataset may be adjusted in amplitude by the inverse of vehicle velocity. As a further non-limiting example, a frequency-domain response of magnitude proximate to a known resonant frequency may be adjusted by the inverse of the square of vehicle velocity.
The underside of cleat 50 is flat, and generally adapted to conform to the surface of the roadway. However, the underside of the cleat can also be configured to couple to the roadway (such as for a roadway including an outwardly projecting coupling feature or a downwardly projecting coupling feature. One example of the former would be a T-shaped bar extending across the roadway and anchored to the roadway. In such a case the underside of the cleat can have the complimentary T-shape, such that the cleat would slide over the bar. Further, the roadway can include a downwardly projecting coupling feature such as a rectangular channel. In such an embodiment the underside of the cleat would have a corresponding rectangular projection that would fit within the channel. Such configurations of the cleat may be useful in those applications in which the cleat is considered not only portable, but also fixed other than by friction to the roadway.
Dimensional and material data was obtained in the open literature regarding American General's standard HMMWV.
The vertical base motions of the front and rear tires are denoted by x1 and x2. The vertical and pitch motions of M3 and Icm3 are denoted by x3 and q, respectively. The nominal parameter values that were used in the model are listed in Table 1.
The lumped parameter set of differential equations corresponding to this model was derived using Newton-Euler methods and is given below:
where c=(b·M2−a·M1)/(M1+M2+M3) and an “*” in the stiffness matrix indicates a symmetric entry in the matrix with respect to the diagonal. A viscous proportional damping model of the form,
[C]=α[M]+β[K], α=0, β=0.02 (2)
is also used in Eq. (1) to describe the dissipative (nonconservative) effects. The functions x1 and x2 were used to model the profile of the cleat, which provides a base excitation to each wheel at different times. x1 and x2 were expressed using a Hanning function of the form:
where h is the height of the cleat, Tc is the time during which a wheel is in contact with the cleat, and Tb is the time it takes for the rear wheel to come into contact with the cleat after the front wheel has reached the cleat. Tc can be calculated using the length of the cleat L and the speed of the vehicle v, Tc=L/v. Likewise, Tb can be calculated using the distance from wheel to wheel (wheelbase) w and the speed, Tb=w/v. x1 and x2 are plotted in
The input-output model in Eq. (1) was then rewritten in state variable form in preparation for conducting time domain simulations. The state vector in this state space representation of the model consisted of the response vector from Eq. (1) and its derivative. The state variable model is given by,
The desired outputs of this model are the forces inside the front and rear tires because the goal of the instrumented cleat is to measure forces in the tire to identify faults in the tires and suspension. Therefore, the output equation used in this state variable model is given by:
The modal properties associated with the free response of the vehicle model were calculated by solving the corresponding eigenvalue problem using the state matrix in Eq. (4). The eigenvalue formulation takes the following form:
where {x} is the modal deflection shape and λ is the corresponding modal frequency (eigenvalue). For the mechanical properties chosen in Table 1, the eigenvalue problem in Eq. (6) was solved and the modal properties obtained are listed in Table 2. The first two modes of vibration are associated with the sprung mass (pitch and bounce) and the second two modes are associated with the wheel hop resonances of the front and rear. The modal deflection shapes are only indicated to two significant digits to highlight the dominant degrees of freedom in each mode shape. The four undamped natural frequencies are at 0.63, 0.88, 7.90, and 7.92 Hz. Consequently, when the base excitation functions shown in
To examine the forces that are produced in the tires of the vehicle as the front and rear wheels traverse the cleat, the Bode diagrams relating the input displacements to the wheels (x1 and x2) and the forces in the tires (f1 and f2, see Eq. (5)) were constructed. The Matlab® bode function was used to produce these diagrams. These diagrams relate the amplitudes and phases of the input displacements to the amplitudes and phases of the forces measured within the instrumented cleat, which is proposed for use in diagnosing vehicle faults.
The modal frequencies given above for the sprung vehicle mass are evident in the peaks of the Bode magnitude plots. The two wheel hop frequencies are also evident but are much more heavily damped than the bounce and pitch modes as expected from Table 2.
Damage due to fractured suspension tie bolts or faulty struts and tires that are underinflated or contain separated plies were analyzed. First, a 15% reduction in K1 (see
This result is consistent with the location of the damage in the system relative to the deflection mode shapes listed in Table 2. The bounce motion at 4 rad/s (and to a lesser extent in the pitch motion at 5 rad/s) indicate that there is more deflection and velocity across the suspension than in the tire hop deflections. Therefore, these motions of the sprung mass are sensitive to the suspension damage in K1. In contrast, the response in the frequency range above 40 rad/s is most sensitive to changes in the front tire rate, Kf.
The forced response in the time and frequency domains for the excitation functions shown in
The same forced response simulation was performed for a scenario involving a 15% reduction in the front tire stiffness. Then the resulting forced response for this fault in addition to the forced response for the suspension fault were both subtracted from the undamaged forced response. The spectral magnitudes of these differences due to the two distinct faults were plotted as shown in
To examine the effects of a change in the aspect ratio of the cleat, the width was increased by a factor of 2 (24 in) and 3 (36 in), and the change in force was again calculated for the scenario involving only a fault in the front tire. The percentage change in force spectrum was then plotted in
A rubberized cleat 50 was instrumented with two PCB 356A32 tri-axial accelerometers and a small truck was used as the test vehicle 20. These accelerometers were used to measure the responses on the left and right side of the cleat. These responses are indicative of the forcing function that acts through the tire as the vehicle traverses the cleat. The left and right accelerometers 60.2 and 60.1, respectively, were positioned in the center plane of the cleat using metal plugs and cables 72 were run out to the data acquisition system 70 through the base of the cleat. The plugs were installed so that they were not touching the ground to provide measurements that would be sensitive to the forces acting through the tire. The instrumented cleat 50 used in the experiment is shown in
Data is provided from the sensors 60 of cleat 50 to a data acquisition system that in one embodiment includes a computer having memory. The computer includes the electronic signal processing desirable to acquire the signal from sensor 60 and convert it to digital data. This signal conditioning can include various low pass, high pass, or bandpass filters that remove noise from the signals. The output of the signal conditioner is a digital signal representative of the time response of the sensor from the disturbance by the vehicle wheel to the cleat. The digitized time domain signal can be further analyzed in the time domain or frequency domain. Preferably the latter is performed by way of a Fourier transformation, such as by an FFT circuit card.
There are yet other sensors that provide signals to the measurement computer in various embodiments, including ambient temperature and cleat temperature. With regards to cleat temperature, in those embodiments using elastomeric cleats, the responses stored in a dataset can be adjusted for the cleat temperature, taking into account that an elastomeric cleat may be stiffer on a cold day or softer on a warm day.
Further, the software of the measurement computer tracks the time of day and location of the cleat, such as by a clock for the former and GPS information for the latter. In some embodiments, the measurement computer keeps track of the identity of the cleat (such as by serial number), and maintains a record of the usage of the cleat (i.e., the number of times that the cleat has been driven over by a vehicle). In such embodiments, an algorithm within the software can inform the operator that the cleat is wearing out, and has used most or all of its useful life. The software of measurement computer further performs diagnoses of the condition of the vehicle, as will be discussed further herein.
In one embodiment of the present invention, especially for those applications in which the resilient properties of the cleat are known to change as a function of time (such as from environmental degradation due to ozone or other compounds) or as a function of usage, the software can adjust any of the response datasets accordingly. For example, for a cleat that has moderate usage but has not reached the end of its useful life, the software can adjust the data of the specific dataset recorded by a vehicle traversing the partially worn-out cleat to account for resilient material that is more flexible. Alternatively, the software could likewise adjust the baseline or family dataset, and/or adjust the fault index for a degraded cleat.
The experiment included of six tests: a first baseline, a simulated suspension fault, three simulated tire faults, and a second baseline. The baseline vehicle had no faults and the pressure in all four tires was 35 psi. The fault in the vehicle suspension was simulated by inserting a metal spacer into the front right coil spring 26.1 of the vehicle 20 as shown in
Each test consisted of the vehicle being driven over the instrumented cleat at 5 mph five times and the average accelerations were calculated from the measured data. The data was initially sampled at 16,384 Hz and then down sampled to 819.2 Hz to highlight the lower frequency content that is more indicative of the wheel end and suspension response.
First, the suspension fault simulated as shown in
The peak at 7.5 Hz is associated with one of the suspension modes probably at 10 Hz in the other two datasets. The modal peak when the metal spacer is inserted is lower in frequency because by splitting the coil spring of stiffness k into two shorter coil springs of stiffness k, the resultant effective stiffness of the spring is lower, e.g., k/2. The peak at 15 Hz is a second harmonic of 7.5 Hz due to the nonlinear response of the suspension as the spring coils compress on the metal spacer. This behavior was not modeled in the simplified model of
The fault index 88 is a quantitative measure of the difference between baseline data and data from a specific vehicle under analysis. Baseline data can include response data from the specific vehicle under test, but taken at a time when the vehicle is considered to be an unfaulted configuration, such as when the vehicle left its new build assembly line, when it left as a repaired and rebuilt vehicle from a depot, or even at some point in time after usage of the vehicle began, as examples. In some cases the baseline data is a baseline for a family of vehicles, wherein the term “family” includes vehicles of the same name or part number. When the baseline data includes multiple vehicles, or when it includes multiple data sets from a particular vehicle, then the baseline data can be quantified statistically in terms of high and low response at a particular frequency, for a vehicle being driven at a particular velocity. The present invention further contemplates those embodiments in which the baseline data is simplified to a range of responses at a particular vehicle speed. It is also understood that the present invention contemplates embodiments in which the baseline data is expressed statistically, such as in terms of mean, median, and standard deviation.
The present invention contemplates any manner of fault index in which a dataset from a specific is compared to a baseline dataset. As one example, the baseline dataset and the specific dataset can be analyzed in the frequency domain, such as by means of a transformation of the time-based data with Fourier transformation. As one example, the baseline and specific Fourier components can be compared at any of the known resonant modes of the chassis-suspension system. Further, the fault index can include comparison of frequency components that are not at or near resonant frequencies, such as those that could be induced by a fault in a subframe or frame of the vehicle. Further, the fault index could be prepared in terms of a shift in frequency for a resonant mode.
Yet other embodiments of the present invention contemplate analysis of the fault index in the time domain. As one example, the fault index could be based on a comparison of terms of peak acceleration, peak velocity, peak displacement, peak strain, and the like. Further, the fault index could be based on the comparison of data in the time domain in a particular time window, such as within a window of predetermined time, the window having a beginning based on when the first motion is detected by sensor 60, as one example.
To verify that this approach of
Various other embodiments of the present invention pertain to instrumented cleats that are chevron-shaped or placed at an oblique angle relative to the direction of preferred travel on the roadway.
A simplified four degree of freedom model of a HMMWV was developed to study changes in the forces in the tires as a function of faults in the wheels and suspensions. Simulations showed that tire faults were more readily detected than suspension faults at lower frequencies using measured forces in a roadway cleat. Longer cleats were shown to produce data that better separated healthy and faulty wheel end and suspension responses. Tests on a small truck showed that a simulated suspension fault could be detected and isolated to the front right corner of the suspension using an instrumented rubberized cleat to measure tire forces.
Yet other embodiments of the present invention include multiple patterns of cleats that are adapted and configured to excite one or more of the resonant frequencies of the vehicle system (as determined by analysis of a model as shown in
An additional experiment was conducted with one embodiment of the present invention with a rubber cleat 50, which was instrumented with two tri-axial accelerometers (
Yet other embodiments of the present invention pertain to a method for calibrating the sensors of an instrumented cleat. Referring to
The response of a cleat to being driven over by a vehicle depends, at least in part, on the velocity of the vehicle. In terms of the directional component of the vehicle velocity vector, a vehicle driving onto a cleat placed perpendicularly relative to the centerline of the roadway will have its two front wheels ride over the entrance, transition, and exit of the cleat at substantially the same moments in time. However, if the velocity vector is skewed at a non-perpendicular angle relative to the cleat, then one wheel will strike the entrance to the cleat before the other wheel. In situations where the angle of attack is non-perpendicular, it is possible that in some configurations of cleat there could be a traveling wave from one of the sensor locations to the other sensor location that arrives at about the same time as the second sensor is impacted by the vehicle wheel. In some embodiments of the present invention and especially for those cleats in which a traveling wave of non-negligible magnitude can be expected, it may be helpful to detect the traveling wave and apply some type of compensation to affected sensor. In yet other embodiments it may be useful to assume a time delay, calculate compensation, and then review the compensated values to determine the probability of interference with a traveling wave. In yet other embodiments it may be useful to establish the expected range of vehicle velocities such that cross talk effects are minimized.
In yet other embodiments, such as with the cleat shown in
The additional experiments consisted of five tests: two baselines (initial and final), two simulated suspension faults, and one simulated tire fault. The final baseline test was conducted after all other tests had been completed. The baseline condition consisted of front tire pressures of 20 psi and rear tire pressures of 22 psi. The two suspension faults were simulated by inserting a metal wedge into the front-right and rear left suspension coil springs. The tire pressure test was conducted by reducing the tire pressure in the front-right tire to 14 psi.
As can be seen in
Accelerometer 60.2 is the first to register a response as the vehicle travels in the East bound direction over the cleat 50. The average data acquired across 10 tests for the X, Y, and Z directions of acceleration are plotted in
As the vehicle continues to move forward, accelerometer #1 registers its transient response as shown in
These two results taken together suggest that the direction of travel of the vehicle can be determined if the vehicle approach direction is not perpendicular to the line between accelerometers #1 and #2. This ability to determine the direction of travel could be important from an operational perspective. For instance, a vehicle traveling out of the depot could be distinguished from one that is traveling into the depot for service and maintenance using only one cleat based on this approach.
The frequency response function relating a force in the left wheel to the response of accelerometer #2 is denoted by H2(ω), and the corresponding frequency response function for the right wheel near accelerometer #1 is denoted by H1(ω). It is assumed that the frequency response functions that relate input forces from the tire footprint to output acceleration responses in the cleat are equal for the vehicle traveling in the East and West bound directions. Given these assumptions, the equations relating the measured accelerations A1e(ω) and A2e(ω) for East bound travel and A1w(ω) and A2w(ω) for West bound travel are given by:
A1e(ω)=H1(ω)FR(ω)
A2e(ω)=H2(ω)FL(ω)
A1w(ω)=H1(ω)FL(ω)
A2w(ω)=H2(ω)FR(ω) (7a, b, c, d)
Therefore, the following relationships between the frequency response functions and forces that were estimated on the right and left hand sides of the cleat can be derived:
These formulae were used to calculate and plot the ratios for the left and right hand sides of the cleat to develop insight about the cleat and vehicle symmetry. The initial baseline data for East and West bound directions were used.
There is amplification of the Y direction response in accelerometer #1 relative to accelerometer #2 in the 1000-2000 Hz range. The spectra shown in
To calculate a fault index, the averaged spectra in the 700-900 Hz range for the ten initial baseline accelerations in the X, Y, and Z directions for accelerometers #1 and #2 as the front wheels traversed the cleat were subtracted from each of thirty comparison datasets as a function of frequency. Then this difference was divided by the standard deviation across the ten initial baseline datasets. Finally, the maximum values of these normalized statistical features were calculated and plotted in
The top plot shows the results for accelerometer #1 and the bottom plot shows the results for accelerometer #2. For the first fifteen datasets, which correspond to the initial and final baseline conditions for which there no tire and suspension subsystem faults, there are no deviations outside ±2σ (zero false-positives). For the left-front suspension fault, 4 out of 5 faults are detected by the X, Y, and Z directions using accelerometers #1 and #2. For the left-rear suspension fault, 5/5 faults were detected and for the right-front tire fault, 5/5 faults were detected. Based on the features in
Various embodiments of the inventive cleats discussed herein include one or more axes of measurement. Preferably, an instrumentation package 60 includes one movement sensor oriented in the generally vertical direction, a second movement sensor oriented to detect responses in the generally fore and aft direction and a third movement sensor oriented to detect responses in the lateral direction. However, yet other embodiments of the present invention include only two sensors (such as with vertical and fore and aft orientation).
Yet other embodiments of the present invention contemplate a cleat with a single axis of measurement that is selected to detect certain faults in a vehicle. As one example, a pathway 922 can include first, second, and third instrumented cleats 50X, 50Y, and 50Z. Cleat 50X includes a sensor 60X adapted and configured to detect responses in the X direction. Cleat 50Y includes a sensor 60Y adapted and configured to detect responses in the Y direction. Cleat 50Z includes a sensor 60Z adapted and configured to detect responses in the Z direction. Further, cleats 50X, 50Y, and 50Z may also have cross sectional shapes further optimized to induce responses in the respective dimensions. For example, cleat 50X may be of a chevron-type shape so as to induce lateral responses in the X direction (referring to
Yet other embodiments of the present invention include calculation of an acceleration vector of maximum magnitude at any instant in time. As one example, the separate three axes of measurement can be combined by use of vector addition to calculate a maximum angle of movement response as well as its orientation (such as in terms of angles of roll, pitch, and yaw, or similarly in terms of azimuth and elevation). By calculating a vector of maximum response as a function of time, errors in the initial alignment of the sensors (such as when the triaxial accelerometer and its attaching cup are inserted into the body of the cleat) can be mathematically removed prior to preparing a fault index. In this manner, the fault index is less susceptible to errors and instrument alignment.
Consider the quarter-car model illustrated in
In order to estimate the usage of the mechanical elements represented in
(1) The model can be used to estimate the actual inputs to the wheels from the terrain 23 taking into account the complex tire-terrain interactions. These inputs will vary in terms of their amplitudes and frequencies in different missions; therefore, the model can be used to identify these variations.
(2) The model can be used to identify the presence of degradation in the mechanical elements of the system (e.g., K1, C2) directly. Without this model, changes in measured response data can still be calculated, but these changes may merely be due to changes in the input spectrum resulting in false diagnoses of damage to the vehicle.
The model corresponding to the vehicle system model shown in
The impedance matrix on the left hand side of this equation can then be inverted yielding the frequency response function matrix, which relates the base excitation spectrum to the displacement spectra:
Eq. 10(d) is the dynamic model for the quarter-car model relating the input base excitation spectrum to the output displacement spectra. If all of the mass, damping, and stiffness parameters were known a priori, this model could be constructed and then used as described above for estimating vehicle usage and damage. However, the parameters vary for a number of reasons including varying payloads, vehicle-to-vehicle differences, etc.
Because of these variations, a model identification process can be used in the field to estimate the frequency response functions in Eq. 10(d).
Once the two frequency response functions are estimated in this simplified model as the vehicle exits the motor pool, the vehicle then deploys on a mission. On this mission, the vehicle traverses various terrains 23, which exercise the vehicle 20 differently depending on the vehicle speed and terrain profile. On-board sensors 27 record the operational unsprung and sprung mass displacements (accelerations), and then measurements are fed into the inverse model shown in the bottom left portion of
When the vehicle returns to the motor pool, the diagnostic cleat 50 can again be used not only to inspect the vehicle for possible faults based on the model obtained when the vehicle exited the motor pool, but the cleat can also be used to update the frequency response function model. In this way, the cleat measurements are combined with the on-board operational measurements to carry out a continuous process of model identification and terrain estimation.
Additional information can also be gleaned from the operational field data as shown in
In this manner described above for various embodiments, damage to the vehicle can be identified in addition to the terrains encountered by the vehicle to provide additional information for maintaining the vehicle when it returns to the depot.
While the inventions have been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.
Claims
1. A method for analyzing a vehicle, comprising:
- providing a roadway including a localized elevational change comprising at least one of a bump or trough, a sensor located in the roadway and proximate to the elevational change, and a vehicle having a wheel;
- driving the vehicle such that the wheel rides over the elevational change;
- preparing a first dataset of the response of the sensor to said driving;
- operating the vehicle for a period of time after said driving;
- redriving the vehicle such that the wheel rides over the elevational change after said operating;
- preparing a second dataset of the response of the sensor to said redriving; and
- comparing the second dataset to the first dataset.
2. The method of claim 1 wherein said driving is within a range of predetermined velocities, and said redriving is within the range of predetermined velocities.
3. The method of claim 1 wherein said driving is at a first velocity, said redriving is at a second velocity different than the first velocity, and which further comprises modifying one of the first dataset or the second dataset to account for the difference between the first velocity and the second velocity.
4. The method of claim 1 which further comprises determining changes in the condition of the vehicle by said comparing.
5. The method of claim 4 wherein the wheel is coupled to the vehicle by a suspension, and said determining is of changes in the suspension or the wheel.
6. The method of claim 1 wherein the sensor is an accelerometer.
7. The method of claim 6 wherein the first dataset and the second data set are each expressed in the frequency domain.
8. The method of claim 1 wherein the sensor is a multiaxis accelerometer.
9. The method of claim 8 wherein the first dataset and the second dataset each include maximum acceleration calculated by vector addition of the multi-axis measurements.
10. The method of claim 1 wherein the elevational change is resilient and the sensor is embedded in the elevational change.
11. The method of claim 1 wherein the vehicle has first and second front wheels, and which further comprises:
- arranging the elevational change on the roadway at an oblique angle relative to the centerline of the roadway;
- measuring a time delay with the sensor from the first wheel driving over the elevational change to the second wheel driving over the elevational change; and
- calculating the velocity of the vehicle during said redriving from the time delay.
12. A system for analyzing a wheeled vehicle driven on a roadway, comprising:
- a portable segment of driving surface, said portable segment having a bottom side adapted and configured to be placed on the roadway and a top side adapted and configured for supporting a wheel of the driven vehicle, said portable segment having a cross-sectional shape for changing the elevation of the driven surface;
- a sensor located within said portable segment, said sensor providing a signal corresponding to movement of said portable segment; and
- a computer having software and receiving said signal, said software including a predetermined dataset;
- wherein said software compares the signal to the predetermined dataset.
13. The system of claim 12 wherein said sensor provides a signal corresponding to acceleration within said segment.
14. The system of claim 12 wherein said sensor provides a signal corresponding to strain within said segment.
15. The system of claim 12 wherein said sensor provides a signal corresponding to velocity within said segment.
16. The system of claim 12 wherein said sensor provides a signal corresponding to displacement within said segment.
17. The system of claim 12 wherein the predetermined dataset includes data for a vehicle driven over the same cross-sectional shape.
18. The system of claim 12 wherein the cross sectional shape is a truncated triangle.
19. The system of claim 12 wherein said segment is fabricated from an elastomeric material.
20. The system of claim 12 wherein said segment has a chevron shape as viewed from above.
21. The system of claim 12 wherein said segment has an elongated planform shape, the roadway has a centerline, and said segment is placed on the roadway at an oblique angle relative to the centerline.
22. An apparatus for a vehicular roadway, comprising:
- a portable segment of driving surface, said segment having a bottom side adapted and configured to be placed on the surface of a roadway, said segment having a top surface adapted and configured to be driven on by a wheeled vehicle, said segment having a cross-sectional shape adapted and configured to locally elevate a vehicle driven over said segment, said segment being sufficiently flexible to generally conform to the surface of the roadway; and
- at least two movement sensors located within said portable segment, each of said movement sensors providing a signal corresponding to one of displacement along a direction, velocity along a direction, or acceleration along a direction, the direction of each said sensor being aligned to provide a signal that is at least partly orthogonal to the direction of the signal of the other said sensor.
23. The apparatus of claim 22 which further comprises a plurality of said portable segments each including at least two movement sensors, said segments each having a length and placement on the roadway such that only one wheel of a front pair of wheels of the vehicle traverses a segment at one time.
24. The apparatus of claim 22 which further comprises a plurality of said portable segments each including at least two movement sensors, said segments being arranged in a first group each spaced apart a first distance from one another along the left side of the roadway and a second group each spaced apart a second distance from one another along the right side of the roadway.
25. The apparatus of claim 24 wherein the first distance is the same as the second distance.
26. The apparatus of claim 24 wherein the vehicle has a first frequency of oscillation, and the first distance is selected to excite the driven vehicle at the first frequency.
27. The apparatus of claim 24 wherein the first distance is different than the second distance.
28. The apparatus of claim 24 wherein the vehicle has a first mode of oscillation at a first frequency, a second mode of oscillation different than the first mode at a second frequency, the first distance is selected to excite the driven vehicle at the first mode, and the second distance is selected to excite the driven vehicle at the second mode.
29. The apparatus of claim 22 wherein the cross-sectional shape has a vertical plane of symmetry.
30. The apparatus of claim 22 wherein the bottom side is substantially flat, said segment has a leading edge and a trailing edge and the cross-sectional shape increases to a maximum thickness intermediate of the leading and trailing edges.
31. The apparatus of claim 22 wherein said portable segment is fabricated from an elastomeric material.
32.-48. (canceled)
49. A method for testing a vehicle, comprising:
- providing a portable resilient elevational change including a pair of spaced apart movement sensors and a wheeled vehicle;
- placing the elevational change on a roadway;
- driving the vehicle over the change in a first direction;
- recording first data from each sensor during said driving;
- redriving the vehicle over the change in a second direction generally opposite to the first direction;
- recording second data from each sensor during said redriving; and
- comparing the first data to the second data.
50. The method of claim 49 wherein said first driving and said second driving are at substantially the same speed.
51. The method of claim 49 which further comprises measuring the speed of the vehicle during said driving and during said redriving, modifying the first data based on the speed during said driving, and modifying the second data based on the speed during said redriving.
52. (canceled)
53. The method of claim 49 wherein the movement sensors are accelerometers.
54. The method of claim 49 wherein each of said movement sensors are multiaxial and measure data along at least two axes.
55. The method of claim 54 wherein said comparing includes calculating a vector of maximum magnitude from the multiaxial data of the sensors.
56.-67. (canceled)
68. The system of claim 12 wherein said segment has a serial number, the serial number is stored in said software, and said software records the number of events in which a vehicle has been driven over said segment.
69. The system of claim 68 wherein said software applies a correction to data from the signal based on the number of events.
70. The system of claim 68 wherein said software provides an indication of the remaining life of said segment based on the number of events.
71. (canceled)
72. The method of claim 49 wherein the first data and the second data include acceleration as a function of frequency, and said comparing is dividing the first data by the second data.
73. The method of claim 49 wherein the first data and the second data include acceleration as a function of frequency, and said comparing is subtracting the first data from the second data.
74. The method of claim 49 wherein the sensors are first and second sensors, and said comparing is of the first data of the first sensor with the second data of the first sensor.
75. The method of claim 74 wherein the first data and the second data include acceleration as a function of frequency.
76. The method of claim 74 wherein the first data and the second data include peak responses from the first and second sensors.
77. The method of claim 74 wherein the first data and the second data include average responses from the first and second sensors.
78.-82. (canceled)
Type: Application
Filed: Sep 22, 2009
Publication Date: Oct 20, 2011
Applicant: PURDUE RESEARCH FOUNDATION (West Lafayette, IN)
Inventors: Douglas E. Adams (West Lafayette, IN), Tiffany Lynn Di Petta (Rochester, MI), David Joseph Koester (Lafayette, IN), Grant A. Gordon (Peoria, AZ)
Application Number: 13/120,218
International Classification: G06F 19/00 (20110101); G01M 17/007 (20060101);